Plasmodium lophurae is a protozoan parasite and is the causative agent of malaria in birds. Like all strains of Plasmodia, it has a complex life cycle which has been studied in some detail. See, e.g., Aikawa, Exp. Parasitol 30:284-320 (1971); Aikawa et al., J. Cell. Biol. 77:72-82(1972).
During the intraerythrocytic stages of development of P. lophurae, synthesis of a major protein occurs which eventually accumulates to comprise at least 50% of the cellular mass of the parasite. This protein is a basic polypeptide of about 45 kilodaltons, and is comprised of about 73% histidine. It is referred to as the "Histidine Rich Protein (HisRP). In this regard, see Kilejian, J. Biol. Chem. 249:4650-4655 (1974).
Recently, the gene expressing P. lophurae HisRP has been cloned. Ravetch et al., Nature 312:616-620 (1984). The disclosure of the Nature paper is incorporated by reference herein.
Due to the similarity in life cycles of different strains of Plasmodia, it was thought that possibly analogous HisRP was produced by other strains of Plasmodia responsible for malaria in other species. In particular, Plasmodium falciparum, the causative agent of malaria in humans, was studied.
It has been learned that a HisRP is in fact produced by P. falciparum, and that two variants are produced. One is associated with what is referred to as "knobby phenotype" (K.sup.30 ); Kilejian, Proc. Natl. Acad. Sci. 76:4650-4653 (1979); and "knobless phenotype" (K.sup.-); Schmidt et al. J. Clin. Invest. 70:379-386 (1982). The "knobby" and "knobless" phenotypes have been implicated in cytoadherence, which is characteristic of erythrocyte infection. Trager et al. Bull. W.H.O. 35:883-885 (1966); Luse et al., Am. J. Trop. Med. Hyg. 20:655-660 (1971).
It has now been found that cDNA expressing both K.sup.+ and K.sup.- HisRP can be obtained by the use of P. lophurae HisRP expressing DNA. The implication of such a discovery are of great interest and value to those in the art, as will be evident from review of the disclosure which now follows.